Acrylamide polymers are applied to coagulants, thickeners for paper making, and the like. For each use, an acrylamide polymer having high-molecular mass, high solubility, and almost colorless color tone has been desired.
For example, if a low-molecular mass acrylamide polymer is used as a coagulant, the acrylamide polymer imparts an insufficient aggregative property. If an acrylamide polymer having poor solubility is used as a coagulant, a problem of delay of treatment time is arisen. If an acrylamide polymer having poor solubility is used as a thickener for paper making, a defect such that fish-eye generates on the paper occurs. When the acrylamide polymer is used as a thickener for paper making, as a matter of course, it is necessary to use an acrylamide polymer having almost colorless color tone.
Under such a condition, regarding improvement of the solubility of an acrylamide polymer, it has been found that acrylamide is produced and an acrylamide polymer is produced by using the acrylamide as a raw material after removing impurities in acrylonitrile. Regarding a method for producing acrylamide, it is known that an enzymic method using a microbial catalyst is preferably adopted (for example, see Patent Documents 1 and 2).
When acrylamide is produced by the enzymic method, various studies have been carried out for improving the quality of acrylamide polymers. For example, a method of limiting a usage of a catalyst (Patent Document 3), and a method of removing impurities derived from a catalyst in a produced acrylamide aqueous solution (Patent Document 4) are known.
However, an acrylamide polymer produced using, as a raw material, acrylamide obtained by the enzymic method using a microbial catalyst has insufficient molecular mass and solubility, and color tone thereof is not colorless.
Regarding the enzymic method, there are almost no reports about a pump to be used when acrylamide is produced. Only Patent Document 5 discloses a method for producing an acrylamide aqueous solution by hydrating a reaction mixture containing acrylonitrile in an aqueous solution while circulating the aqueous solution using a side channel pump (a kind of centrifugal pumps) in the presence of a microbial catalyst.
However, an acrylamide polymer produced using, as a raw material, the acrylamide obtained by the above method has insufficient molecular mass and solubility, and color tone thereof is not colorless.
Patent Document 1: Japanese Unexamined Patent Application, First Publication No. H10-316714
Patent Document 2: Japanese Unexamined Patent Application, First Publication No. H9-118704
Patent Document 3: Japanese Unexamined Patent Application, First Publication No. 2001-299376
Patent Document 4: Japanese Unexamined Patent Application, First Publication No. 2001-078749
Patent Document 5: Japanese Unexamined Patent Application, First Publication No. 2004-524047